Field of the Invention
The invention relates to a transmission which comprises a drive train having a primary drive with a primary drive shaft, especially for a vehicle, and which comprises a Ravigneaux planetary gear set which has a double planetary gear with two sun gear shafts, one planetary carrier shaft and at least one ring gear shaft, as well as an upstream single planetary gear set which is arranged as a reduction gearing and comprises the gear elements of sun gear, planetary carrier and ring gear, wherein a first of said gear elements of the single planetary gear is designed to be fixed to a housing. The invention further relates to a method for operating the transmission.
The Prior Art
A transmission of the kind mentioned above is known from U.S. Pat. No. 5,106,352 A. Such so-called Lepelletier transmissions are used for example in automatic transmissions of vehicles and represent a further development of the so-called Ravigneaux set—a double planetary gear. The Lepelletier set is produced in that a Ravigneaux set is preceded by a further single planetary gear and is connected by clutches. The ring gear of the single planetary gear is permanently connected to the engine drive shaft. This means that the single planetary gear set is always co-rotated even in idle running. The power take-off occurs via the ring gear of the Ravigneaux set and is connected via the differential gear to the drive wheels. The sun gear of the single planetary gear set is permanently blocked. It is disadvantageous that a large number of clutches and brakes as well as separate acceleration devices used for acceleration such as a hydrodynamic torque converters or the like are required.
DE 10 2004 053 044 A1 discloses a transmission for a hybrid drive having a double planetary gear set and a single planetary gear set, wherein each sun gear shaft of the double planetary gear set is drive-connected to one respective electric machine.
It is the object of the invention to avoid the aforementioned disadvantages and to achieve high functionality in a transmission of the type mentioned above with little effort and little need for space.